Iris diaphragm and blade therefor

ABSTRACT

An iris diaphragm for determining the size of an aperture in photographic equipment. The diaphragm includes a plurality of blades of flat sheet material of arcuate configuration. Each blade extends along an arc of a circle and has an inner concave edge and an outer convex edge. Also each blade has a pair of radial projections projecting radially beyond the outer convex edge. Each blade carries a pair of pins respectively projecting from opposed faces of each blade at the radial projections thereof, with one of these pins forming a pivot pin for each blade and the other of the pins forming a swing pin circumferentially displaced about the pivot pin during swinging of each blade to adjust the size of the aperture. The several blades are consecutively arranged in circumferentially overlapping relationship and respectively supported for swinging movement about their pivot pins while an adjusting means coacts with the swing pins to swing the blades between a position of maximum aperture where they provide a maximum aperture of circular configuration and a position of minimum aperture completely closing the aperture so that no light can pass through the diaphragm in its position of minimum aperture. Each blade has at least one circumferentially extending end projection projecting circumferentially beyond one of the radial projections and coacting with the other blades for maintaining the several blades respectively only in their own planes without permitting the blades to abut at their inner or outer edges.

United States Patent Moriyama [151 3,685,418 51 Aug. 22, 19 72 [54] IRIS DIAPHRAGM AND BLADE THEREFOR [72] Inventor: Itsuki Moriyama, Tokyo-to, Japan [73] Assignee: Asahi Kogaku Kogyo Kabushiki Kaisha, Tokyo-to, Japan [22] Filed: Oct. 30, 1970 [21] Appl. No.: 85,642

[30] Foreign Application Priority Data Dec. 13, 1969 Japan ..44/118010 [52] US. Cl. ..-....95/64 R [51] Int. Cl. ..G03b 9/06 [58] Field of Search ..95/64 R [56] References Cited V UNITED STATES PATENTS 3,438,316 4/1969 Rodier ..95/64 R 2,556,546 6/1951 Lee ..95/64 R 2,944,477 7/1960 Tesch ..95/64 R 1,676,595 7/1928 Wittel ..95/64 R X 1,350,388 8/1920 Podjevin ..95/64 R X FOREIGN PATENTS OR APPLICATIONS 362,598 7/1962 Switzerland ..95/64 R Primary Examiner.loseph E. Peters, Jr. Att0rneySteinberg & Blake [57] ABSTRACT An iris diaphragm for determining the size of an aperture in photographic equipment. The diaphragm includes a plurality of blades of flat sheet material of arcuate configuration. Each blade extends along an arc of a circle and has an inner concave edge and an outer convex edge. Also each blade has a pair of radial projections projecting radially beyond the outer convex edge. Each blade carries a pair of pins respectively projecting from opposed faces of each blade at the radial projections thereof, with one of these pins forming a pivot pin for each blade and the other of the pins forming a swing pin circumferentially displaced about the pivot pin during swinging of each blade to adjust the size of the aperture. The several blades are consecutively arranged in circumferentially overlapping relationship and respectively supported for swinging movement about their pivot pins while an adjusting means coacts with the swing pins to swing the blades between a position of maximum aperture where they provide a maximum aperture of circular configuration and a position of minimum aperture completely closing the aperture so that no light can pass through the diaphragm in its position of minimum aperture. Each blade has at least one circumferentially extending end projection projecting circumferentially beyond one of the radial projections and coacting with the other blades for maintaining the several blades respectively only in their own planes without permitting the blades to abut at their inner or outer edges.-

9 Claims, 4 Drawing Figures PATENTEDMIBZZ I912 3.685418 ENVENTOR /7'SU/(/ MOR/YAMA BY ATT RNEYS IRIS DIAPHRAGM AND BLADE THEREFOR BACKGROUND OF THE INVENTION The present invention relates to diaphragms for photographic devices.

In particular, the present invention relates to iris diaphragms.

When photographing motion pictures of any type, such as for projection upon stationary screens or for television purposes, certain techniques are used in order to maintain the continuity from one scene to the next. One of these techniques is known as a fade-out according to which the scene becomes gradually darkened until it disappears. Another technique is a fadein technique according to which a scene starts with complete darkness and becomes gradually brighter. A third technique is an overlap technique which combines both of the above techniques. Diaphragms of the objectives of motion picture cameras are conveniently used for carrying out the fade-in and fade-out techniques.

Such diaphragms are conventionally iris diaphragms according to which a plurality of arc-shaped blades are arranged in consecutively overlapping relationship and circumferentially disposed so that rotary movement of an adjusting ring swings the blades for selectively opening or closing the aperture defined thereby. Conventional diaphragms of this type are not capable of completely closing the aperture because the inner and outer edges of the blades, particularly during closing of the aperture, come into abutment against each other with an edge of one blade butting against an edge of another blade, providing between the blades an unavoidable interference which makes it impossible to achieve a complete closure of the aperture.

This difficulty encountered with conventional iris diaphragms limits the use thereof for fading techniques of the type referred to above. If such diaphragm is used only for a fade-out or only for a fade-in, it is still possible to obtain a satisfactory result because the minimum aperture is relatively small. However, when utilizing the overlap of fade-out and fade-in, the part of the film previously exposed during the fade-out operation is retracted and again exposed during the subsequent fade-in operation. This retraction of part of the film is carried out with the diaphragm closed. With a conventional diaphragm, because there is still a small aperture at the end of a fade-out, the retracted part of the film is doubly exposed through this small aperture during retraction of part of the film in preparation for a subsequent fade-in when the overlap technique is used.

This problem has been recognized and various expedients are known for attempting to avoid this problem. Thus, it has been proposed to provide diaphragms consisting of only two blades, in order to achieve complete closure of the diaphragm at the end of a fade-out operation. Also, it has been proposed to provide additional blades used exclusively for closure of the diaphragm, such blades being arranged just before and just behind the diaphragm and acting independently of normal adjustment of the exposure aperture. Such additional blades can be moved so as to cover the aperture completely when the diaphragm is set at its minimum aperture. Also it has been proposed to provide a spacer plate between each pair of successive blades in order to prevent the edges of one blade from interfering with the edges of another blade, particularly during actuation of the diaphragm to carry out a fadeout operation.

All of the above attempts to solve the problem have proved to be unsatisfactory in practice. Thus, an arrangement where the diaphragm consists of only two blades has serious disadvantages when the diaphragm is used to provide an aperture of selected size for normal photography purposes. Use of additional blades exclusively for achieving full closure of the aperture has proved to be disadvantageous in that it is still possible for some light to pass through gaps between the iris diaphragm blades and the additional blades provided exclusively for aperture closing purposes. The arrangement according to which spacer plates are provided between consecutive blades is disadvantageous in that the possible number of diaphragm blades which can be used is greatly limited with such constructions. Ex perience has shown that all of these attempts to solve the problem are impractical and result only in creatio of additional problems.

SUMMARY OF THE INVENTION It is accordingly a primary object of the invention to provide a diaphragm which can be very effectively used for an overlap of fade-out and fade-in without any danger of exposing film undesirably during retraction of the part thereof which is to have the fade-out followed by a fade-in.

In particular, it is an object of the present invention to provide a diaphragm with blades which consecutively overlap each other but which at the same time reliably remain in their own planes in which they swing without any one blade extending into a plane occupied by another blade.

A further object of the present invention is to provide diaphragm blades which are constructed in such a way that they cannot be improperly oriented in the diaphragm assembly.

Furthermore, it is an object of the present invention to provide for a diaphragm of the above type a blade which is of an exceedingly simple and rugged construction so that it can be inexpensively manufactured and at the same time will operate very reliably in the diaphragm assembly.

Yet another object of the present invention is to provide a construction according to which the pins which support the blades for swinging movement and which are actuated to swing the blades are arranged in such a way that no pins engage the peripheries of any blades during adjustment of the diaphragm.

Thus, one of the primary objects of the present invention is to provide a diaphragm with blades which can be swung between a position of maximum aperture where a substantially circular diaphragm aperture is provided and a position of minimum aperture where the diaphragm aperture is completely closed so that no light can pass through the diaphragm when the blades thereof are positioned in the diaphragm closing position.

According to the invention, the diaphragm includes a plurality of blades of flat sheet material, with each blade being of an arcuate configuration and extending along a given circle, Each blade has an inner concave edge to form part of a diaphragm aperture and an outer convex edge. A pair of radial projections project beyond the outer convex edge of each blade and respectively carry a pair of pins which respectively project from opposed faces of each blade, one of these pins being a pivot pin and the other of the pins being a swing pin circumferentially displaced about the pivot pin during swinging of the blade in order to change the size of the aperture. The blades consecutively overlap each other circumferentially in the maximum aperture position of the diaphragm, and each blade has as a part thereof a means which maintains each blade exclusively in its own plane without any blade entering into a plane occupied by any other blade, so that in this way there is no interference or butting of the blades with each other at their peripheral edges during swinging of the blades.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of the application and in which:

F 16.1 is a transverse section taken in a plane normal to the optical axis through the diaphragm adjusting ring and the tubular housing for the diaphragm, FIG.1 illustrating the manner in which the consecutive overlapping diaphragm of blades are positioned with respect to each other when providing the maximum diaphragm aperture;

FIG.2 is a fragmentary longitudinal sectional elevation of part of the structure of P161 taken along line XX of FIG. 1 in the direction of the arrows;

F [G3 is a view similar to FIG. 1 but showing the positions which the blades take in the position of minimum aperture where the diaphragm is completely closed; and

F164 is an elevation of one of the blades of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, F 16.4 illustrates one of the blades of the invention. The several blades which are assembled to form the diaphragm of the invention are all identically constructed, with each blade having the construction shown for the single blade of FIG.4 Referring to FIG.4 it will be seen that each blade is formed of a body A of a relatively thin sheet material, which may be a suitable thin sheet metal, for example. The sheet material A is flat and of an arcuate configuration, extending along a circle, as is apparent from FIG.4 As may be seen from FIG.4 each blade extends through approximately 180 so as to form approximately one-half a circle. Each flat blade has an inner concave edge and an outer convex edge. The inner concave edge forms part of the diaphragm aperture, as will be apparent from the description which follows.

Each blade is also provided with a pair of radial projections projecting radially beyond the outer convex edge, as is apparent from FIG.4 These radial projections respectively carry pins C and C These pins respectively project from the opposed faces of the blade. Thus, as viewed in FIG. 4, the pin C projects toward the viewer from the face which is visible in FIGA while the pin C projects away from the viewer from the face of the blade which is not visible in FIG.4

These pins respectively form a pivot pin and a swing pin for each blade. In the example of FIGA, the pin C is considered as the pivot pin whose axis remains stationary so that the blade swings about this axis, while the pin C is considered as the swing pin and is acted upon by an adjusting means referred to below which brings about swinging of the blade about the pin C Furthermore, in accordance with the invention, each blade is provided with a means for maintaining each blade at all times only in its own plane without permitting any one blade to occupy at any time a plane which is occupied by any other blade. This means forms part of each blade and includes at least one end circumferential projection projecting circumferentially beyond one of the radial projections. Thus, referring to FIG.4, it will be seen that the blade illustrated therein includes a circumferential end projection B which functions 'in a manner referred to in greater detail below to maintain the blade at all times only in its own plane. In the actual structure illustrated, however, each blade has a second circumferential end projection B extending circumferentially beyond the other radial projection, namely to one which carries the pin C It will be noted from FIG.4 that the illustrated blade is of a symmetrical configuration with respect to an axis of symmetry situated in the plane which is occupied by the blade and passing midway between the pair of projections B and B through the center of the concentric circles along which the inner and outer edges of the blade extend. Because of this symmetrical construction and because of the fact that the pins C and C respectively project from the opposite faces of the blade, it is impossible to orient the blade improperly in the diaphragm assembly. In other words, the blade shown in F IG.4 can be reversed end for end so that the projection B occupies the position occupied by the projection B in FIG.4 with the face illustrated in F IG.4 becoming invisible and with the opposed face becoming visible. It will be noted that with such reversal the pin C will occupy the position occupied in FIG.4 by the pin C while the latter pin of FIG.4 will then assume the position shown in FIG.4 for the pin C As a result, when assembling the diaphragm of the invention it is not possible to erroneously orient the blades with pins projecting in opposite directions. These pins C and C are identical so that irrespective of which face of the blade is directed forwardly and which rearwardly, one of the pins is available to function as a pivot for the blade and the other of the pins is available to coact with the adjusting structure for swinging the blade.

These blades of FIG.4 are assembled in the manner shown in FIGS. 1 and 3 so as to form a diaphragm where the blades circumferentially overlap each other in the manner shown in FIG.1 in order to provide the maximum aperture of FIG.1. As was pointed out above, each blade extends through approximately 180. Moreover, as is apparent from FlG.l, there are five blades la, lb, 1c, 1d, and 1e. The extent of overlap of the consecutive blades is such that the blade 1a overlaps the blade lb by approximately so that the latter projects through approximately 90 circumferentially beyond the blade la, while the blade 1c is overlapped through approximately 90 by the blade 1b and projects through approximately 90 beyond the blade 1b. In the same way, the blade 1d is overlapped through approximately 90 by the blade and projects beyond the latter through approximately 90 into a 90 overlapping relationship with respect to the final blade 1e which again projects through approximately 90 beyond the blade 1d. The result is that each three consecutive blades form substantially a complete circle in the maximum aperture position shown in F 10.1.

As may be seen particularly from FIG.2, the diaphragm is situated within the tubular housing or casing 2 of an objective, for example, and this tubular enclosure 2 is provided with an inwardly directed flange or ring 2 formed with openings which receive the several pivot pins C of the several blades. These pins are shown in dotted lines in FIG.l since they extend away from the viewer of FlG.ll, and it will be noted that the several pins C are uniformly distributed angularly about the optical axis, so that the several identical blades are also uniformly distributed angularly about the optical axis.

in order to adjust the diaphragm the several swing pins C are respectively received in relatively short radial slots 8 formed in an adjusting ring 3 having a circumferential outer flange situated in an inner circumferential groove of the tube 2. The wall of the tube 2 at this circumferential groove is formed with an arcuate slot 5 extending through the wall and along the groove which receives the adjusting ring 3 of the diaphragm adjusting ring. A pin 6 projects radially with respect to the optical axis through the slot 5. The pin 6 is fixed at its inner end to the circumferential outer flange of the adjusting ring 3. At its outer end where it projects beyond the tube 2, the pin 6 is fixed with a diaphragm adjusting or setting ring 4 surrounding and accessible at the exterior of the tube and turnable about the latter for adjusting the diaphragm. As is well-known, the ring 4 may carry at its exterior suitable graduations which may be selectively aligned with a given index at the ex terior surface of the tube 2, so that the operator can set the diaphragm to provide a suitable selected aperture.

It will be noted that the length of the slot 5 is such that the pin 6 can be swung from one end to the other end of the slot, from the position of F 10.1 to the position of FIG.3, displacing the diaphragm between the position of maximum aperture shown in FlG.l and the fully closed position of FlG.3 where no light can pass through the diaphragm. It is furthermore to be noted that the location of the pivot and swing pins is such that none of these pins can in any way interfere with the outer convex edges of the diaphragm blades. Thus, the ring 4 can be swung in a counterclockwise direction, as viewed in FIG], from the position of FlG.l into the position of F [6.3 in order to fully close the aperture. in the position of minimum aperture it will be noted that the inner concave edges of the several blades extend at least up to the optical axis. Between the positions of FIGS.1 and 3 it is possible to set the diaphragm to provide any selected aperture for normal photography purposes. However, it is also possible to provide the complete closure of FIGS without any possible abutment of the edges of the blades against each other since they are maintained in their own planes without possibly entering into planes occupied by other blades, as a result of the means formed by at least one of the projections B B As a result of these extensions 8,, B

the extent of overlap of the blades, even at the position of maximum aperture where the overlap is at a minimum, is such that these extensions serve to maintain each blade only in its own plane in which it swings without having the possibility of entering into a plane occupied by any other blade. With this construction turning of the ring 4 will not displace any blade out of the plane which it occupies, so that this factor together with the factor of situating the pins C and C beyond the peripheries of the blades brings about an exceedingly smooth movement of the blades without any possible disturbance therebetween.

The consecutive arrangement of the blades in circumferential overlapping relationship also contributes to preventing the planes occupied by the blades from intersecting each other. It is thus possible to achieve complete closure without any abutment of the peripheral edges of the blades with each other.

With the structure of the invention there is no requirement of additional blades used exclusively for complete closure of the aperture and there is also no limitation on the number of blades which may be used. It thus becomes possible to maintain the substantially circular configuration for the aperture during selective changing of the size thereof in connection with normal photography.

The ring 4 can be used for setting the diaphragm to provide a selected aperture during normal photography or it can be used in connection with achieving complete closure during fade-in and fade-out operations.

What is claimed is:

1. An iris diaphragm comprising a plurality of diaphragm blades each in the form of a flat sheet material of arcuate configuration extending along a given circle through approximately and each having an inner concave edge extending along a circle for defining part of a diaphragm aperture and an outer convex edge, each blade having a pair of radial projections extending beyond said outer convex edge and respectively carrying a pair of pins projecting perpendicularly from each blade, one of said pins projecting from one face of each blade and forming a pivot pin and the other of the pins projecting from an opposed face of each blade and forming a swing pin, said blades partly overlapping each other circumferentially in the position of maximum aperture with each blade directly engaging and located immediately next to the next following blade and forming a maximum aperture of circular configuration with said blades uniformly distributed about an optical axis which contains the center of the aperture, support means coacting with said pivot pins of said blades to support said pivot pins for turning movement about their own axes, respectively, and adjusting means coacting with said swing pins for circumferentially displacing the swing pin of each blade about the axis of the pivot pin thereof, for increasing and decreasing the size of said aperture, said adjusting means coacting with said swing pins for swinging said blades from the position of maximum aperture to a position where the inner edges of said blades extend at least up to said optical axis for completely closing said aperture, and means forming part of each blade and slidably engaging the next following blade for maintaining each blade at all times only in its own plane without entering into a plane occupied by any other blade.

2. The combination of claim 1 and wherein said means for maintaining each blade at all times only in its own plane includes at least one end projection located in the plane occupied by each blade and projecting circumferentially beyond one of said radial projections.

3. The combination of claim 2 and wherein each blade has a'pair of said end projections respectively projecting circumferentially beyond said pair of radial projections.

4. The combination of claim 3 and wherein each blade is of a symmetrical configuration with respect to an axis of symmetry extending centrally between said end projections in the plane of each blade.

5. The combination of claim 4 and wherein said pins are identical so that the faces of each blade do not require a particular orientation.

6. An iris diaphragm comprising a plurality of diaphragm blades each in the form of a flat sheet material of arcuate configuration extending along a given circle and each having an inner concave edge for defining part of a diaphragm aperture and an outer convex edge, each blade having a pair of radial projections extending beyond said outer convex edge and respectively carrying a pair of pins projecting perpendicularly from each blade, one of said pins projecting from one face of each blade and forming a pivot pin and the other of the pins projecting from an opposed face of each blade and forming a swing pin, said blades partly overlapping each other circumferentially in the position of maximum diaphragm aperture and forming a maximum aperture of circular configuration with said blades uniformly distributed about an optical axis which contains the center of the aperture, support means coacting with said pivot pins of said blades to support said pivot pins for turning movement about their own axes, respectively, and adjusting means coacting with said swing pins for circumferentially displacing the swing pin of each blade about the axis of the pivot pin thereof, for increasing and decreasing the size of said aperture, said adjusting means coacting with said swing pins for swinging said blades from the position of maximum aperture to a position where the inner edges of said blades extend at least up to said optical axis for completely closing said aperture, and means forming part of each blade for maintaining the latter at all times only in its own plane without entering into a plane occupied by any other blade, said means for maintaining each blade at all times only in its own plane including a pair of end projections located in the plane occupied by each blade and projecting circumferentially beyond said pair of radial projections, each blade being of a symmetrical configuration with respect to an axis of symmetry extending centrally between said end projections in the plane of each blade, said pins being identical so that the faces of each blade do not require a particular orientation, and each blade extending through an arc of approximately 180, the consecutive overlapping blades being arranged with each blade overlapping the next blade, in the position of maximum diaphragm aperture, through an angle of approximately so that each blade projects circumferentially in the position of maximum aperture beyond the immediately preceding blade by approximately 90, with each three consecutive blades providing in the position of maximum diaphragm aperture substantially a f i h go riib l ria ii ii o i: i i i id idl ierein there are five blades unifomily distributed about the optical axis.

8. For use in an iris diaphragm, a blade composed of a flat sheet material of arcuate configuration extending through approximately along part of a circle and having an inner concave edge extending along a circle for defining part of a diaphragm aperture and an outer convex edge, said sheet material having a pair of radial projections angularly spaced from each other and extending outwardly beyond said outer edge and carrying a pair of pins respectively projecting from opposed faces of said sheet material, and said sheet material including a pair of circumferential end projections projecting circumferentially beyond said radial projections and forming end portions of said inner edge.

9. The combination of claim 9 and wherein said sheet material is of a symmetrical configuration with respect to an axis of symmetry situated in the plane of said sheet material midway between said circumferential end projections. 

1. An iris diaphragm comprising a plurality of diaphragm blades each in the form of a flat sheet material of arcuate configuration extending along a given circle through approximately 180* and each having an inner concave edge extending along a circle for defining part of a diaphragm aperture and an outer convex edge, each blade having a pair of radial projections extending beyond said outer convex edge and respectively carrying a pair of pins projecting perpendicularly from each blade, one of said pins projecting from one face of each blade and forming a pivot pin and the other of the pins projecting from an opposed face of each blade and forming a swing pin, said blades partly overlapping each other circumferentially in the position of maximum aperture with each blade directly engaging and located immediately next to the next following blade and forming a maximum aperture of circular configuration with said blades uniformly distributed about an optical axis which contains the center of the aperture, support means coacting with said pivot pins of said blades to support said pivot pins for turning movement about their own axes, respectively, and adjusting means coacting with said swing pins for circumferentially displacing the swing pin of each blade about the axis of the pivot pin thereof, for increasing and decreasing the size of said aperture, said adjusting means coacting with said swing pins for swinging said blades from the position of maximum aperture to a position where the inner edges of said blades extend at least up to said optical axis for completely closing said aperture, and means forming part of each blade and slidably engaging the next following blade for maintaining each blade at all times only in its own plane without entering into a plane occupied by any other blade.
 2. The combination of claim 1 and wherein said means for maintaining each blade at all times only in its own plane includes at least one end projection located in the plane occupied by each blade and projecting circumferentially beyond one of said radial projections.
 3. The combination of claim 2 and wherein each blade has a pair of said end projections respectively projecting circumferentially beyond said pair of radial projections.
 4. The combination of claim 3 and wherein each blade is of a symmetrical configuration with respect to an axis of symmetry extending centrally between said end projections in the plane of each blade.
 5. The combination of claim 4 and wherein said pins are identical so that the faces of each blade do not require a particular orientation.
 6. An iris diaphragm comprising a plurality of diaphragm blades each in the form of a flat sheet material of arcuate configuration extending along a given circle and each having an inner concave edge for defining part of a diaphragm aperture and an outer convex edge, each blade having a pair of radial projections extending beyond said outer convex edge and respectively carrying a pair of pins projecting perpendicularly from each blade, one of said pins projecting from one face of each blade and forming a pivot pin and the other of the pins projecting from an opposed face of each blade and forming a swing pin, said blades partly overlapping each other circumferentially in the position of maximum diaphragm aperture and forming a maximum apertuRe of circular configuration with said blades uniformly distributed about an optical axis which contains the center of the aperture, support means coacting with said pivot pins of said blades to support said pivot pins for turning movement about their own axes, respectively, and adjusting means coacting with said swing pins for circumferentially displacing the swing pin of each blade about the axis of the pivot pin thereof, for increasing and decreasing the size of said aperture, said adjusting means coacting with said swing pins for swinging said blades from the position of maximum aperture to a position where the inner edges of said blades extend at least up to said optical axis for completely closing said aperture, and means forming part of each blade for maintaining the latter at all times only in its own plane without entering into a plane occupied by any other blade, said means for maintaining each blade at all times only in its own plane including a pair of end projections located in the plane occupied by each blade and projecting circumferentially beyond said pair of radial projections, each blade being of a symmetrical configuration with respect to an axis of symmetry extending centrally between said end projections in the plane of each blade, said pins being identical so that the faces of each blade do not require a particular orientation, and each blade extending through an arc of approximately 180*, the consecutive overlapping blades being arranged with each blade overlapping the next blade, in the position of maximum diaphragm aperture, through an angle of approximately 90* so that each blade projects circumferentially in the position of maximum aperture beyond the immediately preceding blade by approximately 90*, with each three consecutive blades providing in the position of maximum diaphragm aperture substantially a complete circle around the optical axis.
 7. The combination of claim 6 and wherein there are five blades uniformly distributed about the optical axis.
 8. For use in an iris diaphragm, a blade composed of a flat sheet material of arcuate configuration extending through approximately 180* along part of a circle and having an inner concave edge extending along a circle for defining part of a diaphragm aperture and an outer convex edge, said sheet material having a pair of radial projections angularly spaced from each other and extending outwardly beyond said outer edge and carrying a pair of pins respectively projecting from opposed faces of said sheet material, and said sheet material including a pair of circumferential end projections projecting circumferentially beyond said radial projections and forming end portions of said inner edge.
 9. The combination of claim 8 and wherein said sheet material is of a symmetrical configuration with respect to an axis of symmetry situated in the plane of said sheet material midway between said circumferential end projections. 